High performance rock bit grease

ABSTRACT

A lubricant for a drill bit that includes from about 0.1 to about 10 weight percent of at least one nanomaterial, from about 5 to 40 weight percent of a thickener, and a basestock is disclosed.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to a lubricant for lubricating journalbearings in a rock bit for drilling earth formations.

2. Background Art

Rock bits are employed for drilling wells in subterranean formations.Such bits have a body connected to a drill string and a single rollercone or a plurality (typically two or three) of roller cones mounted onthe body for drilling rock formations. The roller cones are mounted onjournals or pins integral with the bit body at its lower end. In use,the drill string and bit body are rotated in the bore hole, and eachcone rotates on its respective journal as the cone contacts the bottomof the bore hole being drilled.

Drill bits are used in hard, often tough formations and, therefore, highpressures and temperatures are encountered. The total useful life of adrill bit is typically on the order of 20 to 200 hours for bits in sizesof about 6 to 28 inch diameter at depths of about 5,000 to 20,000 feet.Useful lifetimes of about 65 to 150 hours are typical. When a drill bitwears out or fails as a bore hole is being drilled, it is necessary towithdraw the drill string to replace the bit which is a very expensiveand time consuming process. Prolonging the lives of drill bits minimizesthe lost time in “round tripping” the drill string for replacing bits.

Replacement of a drill bit can be required for a number of reasons,including wearing out or breakage of the structure contacting the rockformation. One reason for replacing the rock bits includes failure orwear of the journal bearings on which the roller cones are mounted. Thejournal bearings are subjected to very high drilling loads, highhydrostatic pressures in the hole being drilled, and high temperaturesdue to drilling, as well as elevated temperatures in the formation beingdrilled. The operating temperature of the grease in the drill bit canexceed 300° F. Considerable work has been conducted over the years toproduce bearing structures and employ lubricants between the bearingsurfaces that reduce friction, minimize wear and failure of suchbearings.

A variety of grease compositions have been previously employed inattempts to reduce friction and thus reduce wear. U.S. Pat. No.4,358,384 discloses one prior art grease composition that consists of apetroleum derived mineral oil lubricant basestock and a metal soap ormetal complex soap including aluminum, barium, calcium, lithium, sodiumor strontium metals. A lighter, lower-viscosity basestock is generallyemployed to obtain low temperature greases, and a heavier,higher-viscosity basestock is used to obtain high temperature greases.

Without being restricted to any method, in drilling applications, themechanism of lubrication is by way of hydrodynamic lubrication. When atrest, the journal and the journal bearings of a drill bit squeeze outthe lubricant and make direct contact. As the journal begins to rotate,the lubricant is drawn into the space between contacting surfaces toform a fluid wedge there between. As the journal rotation increasesspeed, this fluid wedge pushes the journal off the bearings and forms alubricating film between the contacting surfaces. The film thickness isdetermined by both the rotation speed and load capacity of thelubricant. If a film is too thin, the asperities may make contact with agreater force, resulting in shearing action between the surfaces insteadof a sliding action, which in turn generates heat and wears down thecontacting surfaces.

In order to enhance the lubricating capacity of typical petroleumbasestock greases, anti-wear agents have been typically added. Theanti-wear agents, many of which function by a process of interactionswith the metal surfaces, provide a chemical film which reduces orprevents metal-to-metal contact under high load conditions. U.S. Pat.Nos. 4,358,384, 3,062,741, 3,107,878, 3,281,355, and 3,384,582 disclosethe use of molybdenum disulfide, and other solid additives such ascopper, lead and graphite, which have been employed to attempt toenhance the lubrication properties of oils and greases.

Additives which are useful under extremely high load conditions arefrequently called extreme pressure (EP) agents. These materials serve toenhance the ability of the lubricant base stock to form afriction-reducing film between the moving metal surfaces underconditions of extreme pressure and to increase the load carryingcapacity of the lubricants. The function of the lubricant is to minimizewear and to prevent scuffing and welding between contacting surfaces.When metal asperities make contact with greater force and result inshearing rather than sliding, which in turn generates heat and wearsdown the contacting surfaces, EP additives in the lubricant areactivated by the high temperature resulting from the extreme pressure toreact with the exposed metal surfaces and form a protective coatingthereon.

Additionally, while the basestock grease serves important functions withrespect to friction and wear performance, it is generally inferior withrespect to thermal conductivity. The thermal conductivity of oils, e.g.,mineral oil, polyalphaolefins, ester synthetic oils, etc is typically inthe range of 0.12 to 0.16 W/m*K, and water has a much higher thermalconductivity at 0.61 W/m*K. Many of the additives present in alubricating composition may also act to improve the cooling capabilitiesas compared to a basestock alone. It is well known that metals in solidform have orders-in-magnitude larger thermal conductivities than thoseof fluids. For example, the thermal conductivity of copper at roomtemperature is about 3000 times greater than engine oil or pump oil.Therefore, typical lubricants containing such metallic particlesgenerally exhibit significantly enhanced thermal conductivities relativeto fluids alone.

Efforts to even further improve the thermal capacity of heat transferfluids (coolants) have been attempted by varying the metallic additives,not just in type, but in size as well. The original studies of thethermal conductivity of suspensions were confined to those containingmillimeter- or micron-sized particles. Maxwell's model shows that theeffective thermal conductivity of suspensions containing sphericalparticles increases with the volume fraction of the solid particles. Itis also known that the thermal conductivity of suspensions increaseswith the ratio of the surface area to volume of the particle. UsingHamilton and Crosser's model, it can be calculated that, for constantparticle size, the thermal conductivity of a suspension containing largeparticles is more than doubled by decreasing the sphericity of theparticles from a value of 1.0 to 0.3 (the sphericity is defined as theratio of the surface area of a particle with a perfectly spherical shapeto that of a non-spherical particle with the same volume). Because thesurface area to volume ratio is 1000 times larger for particles with a10 nm diameter than for particles with a 10 μm diameter, a much moredramatic improvement in effective thermal conductivity can be expectedas a result of decreasing the particle size in a solution than canobtained by altering the particle shapes of large particles. Whilenanoparticles have been introduced in typical coolants, in the drillingindustry the only nanoparticles used have been limited to carbon black,which shows a fairly low increase in thermal conductivity.

For additives to prove beneficial in a grease used in a drillingapplication, it is necessary to balance thermal performance, the loadcarrying capacity, and seal/glad wear. Generally, lubricants that reduceseal and gland wear typically lack sufficient film strength, that is,load carrying capacity, and lubricants with sufficient film strengthtend show excessive seal and glad wear, to be used as a drill bitlubricant.

Accordingly, there exists a need for lubricant that exhibits improvedthermal performance, a tight seal, and good load carrying capacity withreduced seal and gland wear.

SUMMARY OF INVENTION

In one aspect, the present invention relates to a lubricant for a drillbit that includes from about 0.1 to about 10 weight percent of at leastone nanomaterial, from about 5 to 40 weight percent of a thickener, anda basestock.

In another aspect, the present invention relates to a roller cone drillbit that includes a bit body, at least one leg extending downward fromthe bit body, wherein each leg has a journal and each journal has abearing surface, a roller cone mounted on each journal, wherein eachroller cone has a bearing surface, a grease reservoir in communicationwith the bearing surfaces; and a lubricating composition in the greasereservoir and adjacent the bearing surfaces, wherein the lubricatingcomposition includes from about 0.1 to about 10 weight percent of atleast one nanomaterial, from about 5 to 40 weight percent of athickener; and a basestock.

In yet another aspect, the present invention relates to a method forlubricating a roller cone drill bit that includes providing a rollercone drill bit having a bit body, a grease reservoir, and at least oneroller cone mounted on the bit body with at least one rotatable journalbearing; and filling the grease reservoir with a lubricant, wherein thelubricant includes from about 0.1 to about 10 weight percent of at leastone nanomaterial, from about 5 to 40 weight percent of a thickener, anda basestock.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a semi-schematic perspective of a rock bit lubricated with alubricant according to the present invention.

FIG. 2 is a partial cross-section of the drill bit in FIG. 1.

DETAILED DESCRIPTION

In one aspect, embodiments of the invention relate to lubricants forhigh temperature applications. As used herein, the term “hightemperature” means that the lubricant will spend at least some time inan environment exceeding 250° F. (121° C.). In particular, embodimentsof the invention relate to lubricants for drill bits, methods forlubricating, and methods for drilling. In various embodiments,lubricants disclosed herein may comprise a basestock, a thickener, andat least one nanomaterial.

Basestocks:

The basestock, or base oil, form the main lubricating component. Oilsare generally classified as refined and synthetic. Refined oils are alsoreferred to as mineral oils or petroleum oils. For example, paraphinicand naphthenic are refined from crude oil while synthetic oils aremanufactured by chemical synthesis. The basestock may be selected fromany of the basestocks known in the art, including a synthetic base oil,a petroleum or mineral oil, or combinations thereof. In someembodiments, a synthetic lubricant basestock may be preferred over apetroleum derived basestock to increase viscosity. In other embodiments,a high viscosity petroleum derived mineral oil basestock may be used.

Suitable synthetic oils for use in a basestock may include syntheticpolyalphaolefins, other hydrocarbon fluids and oils, syntheticpolyethers, poly-esters, alkylene oxide polymers, and interpolymers,esters of phosphorus containing acids, silicon based oils and mixturesthereof. In one embodiment, the basestock may include a high viscosityindex polyalphaolefin based fluid. Suitable polyalphaolefins includethose discussed in U.S. Pat. Nos. 5,589,443, 5,668,092, and 4,827,064,which are incorporated herein by reference in their entirety. Othersuitable synthetic oils include alkylated naphthalenes, such asSynesstic™ AN, which is available from ExxonMobil Corporation (Fairfax,Va.), polybutenes, such as Indopol™ polybutenes which are available fromBP P.L.C. (Warrenville, Ill.), and hydrogenated polybutenes, such asPanalane™ hydrogenated polybutenes, which are available from BP P.L.C.(Warrenville, Ill.).

Suitable mineral or petroleum oils may include naphthenic or paraffinicoil. Other suitable mineral oils may include high viscosity indexhydroprocessed basestock and bio-based esters.

In one embodiment, the basestock may be a blend of mineral oil andsynthetic oil. Specifically, in one embodiment, the basestock may be ablend of 0 to 100% mineral oil and 100 to 0% synthetic oil with anypercentage therebetween, preferably about 50% of each.

Thickeners

Thickeners give a lubricant its characteristic consistency and aresometimes thought of as a “three-dimensional fibrous network” or“sponge” that holds the oil in place.

In one embodiment, the base oil may be thickened with a soap, such assoaps of calcium, aluminum, titanium, barium, lithium, and theircomplexes. Metal complex soaps may include alkali metals, alkaline earthmetals, Group IVB metals, and aluminum. Simple soaps may be formed bycombining a fatty acid or ester with a metal and reacting through asaponification process, with the application of heat, pressure, oragitation. While simple soaps are formed by reacting one single organicacid with a metal hydroxide, complex soaps may be formed by reacting twoor more organic compounds with the metal hydroxide.

In another embodiment, the base oil may be thickened with a non-soap,such as urea, fine silica, fine clay, and/or silica gel. In yet anotherembodiment, the basestock may be thickened with both soap and non-soapthickening agents. While the above description lists several specificthickening agents, no limitation is intended on the scope of theinvention by such a description. It is specifically within the scope ofthe present invention that other soap and non-soap thickening agents maybe used.

Additives:

Additives that are commonly added to lubricants to improve theirperformances may also be added to a lubricant of the present invention.For example, a grease may typically include various additives, such as,additives for lubricity, extreme pressure (EP), antiwear, corrosion,solubility, anti-seize protection, oxidation protection and the like.One of ordinary skill in the art would recognize that various typesadditives may also serve multiple roles, such as, for example, anantiwear additive also serving as an extreme pressure additive orantioxidant. Additionally, many of the extreme pressure additives,antiwear additives, lubricious solids aid serve to improve the loadcarrying capacity of a lubricant. When employed, such additives aretypically present in lubricant formulation in amounts ranging from about1 to about 20 weight percent.

Lubricious solids that may be incorporated in the lubricants disclosedherein may include, for example, molybdenum disulfide, graphite,polarized graphite, carbon black, metals, such as lead, copper, andsilver, metal oxide particles, such as lead oxide, zinc oxide, aluminumoxide, copper oxide, bismuth oxide, and antimony trioxide, carbonnanostructures, and diamond particles. In one embodiment, the at leastone nanomaterial may include at least one lubricious solid. Nanomateriallubricious solids may be added to lubricants disclosed herein in anamount greater than about 0.1, 0.2, 0.3, and 0.5 weight percent in someembodiments, and less than 10, 5, 2, and 1 weight percent in otherembodiments.

Antiwear additives that may be used in the lubricants disclosed hereininclude for example, a metal phosphate, a metal dialkyldithiophosphate,a metal dithiophosphate, a metal thiocarbamate, a metal dithiocarbamate,an ethoxylated amine dialkyldithiophosphate and an ethoxylated aminedithiobenzoatees. Metal thiocarbamates may include leaddiamyldithiocarbamate, molybdenum di-n-butyldithiocarbamate, molybdenumdialkyldithiocarbamate, zinc diamyldithiocarbamate, zincdithiocarbamate, antimony dithiocarbamate. In one embodiment, the atleast one nanomaterial may include at least one antiwear additive.Nanoscale antiwear additives may be added to lubricants disclosed hereinin an amount greater than about 0.1, 0.2, 0.3, and 0.5 weight percent insome embodiments, and less than 10, 5, 2, and 1 weight percent in otherembodiments.

Extreme pressure agents that may be used in the lubricants disclosedherein include for example, bismuth oxide, bismuth hydroxide, andmolybdenum disulfide, bismuth ethylhexanoate, non-metallic sulfurcontaining compounds such as a substituted 1,3,4-thiadiazole,non-metallic chloride-sulfur-phosphorus compounds, molybdenumdi(2-ethylhexyl) phosphorodithioate, molybdenum di-2-ethylhexyldithiophosphate, bismuth dithiocarbamates, hexagonal boron nitride(hBN), zinc- and chlorine-based EP agents, such as Lubrizol™ 885 andLubrizolm 2501, which are both commercially available from The LubrizolCorporation (Wickliffe, Ohio). A single EP additive may be employed, oralternatively, a combination of two or more EP agents may be employed.

In one embodiment, the at least one nanomaterial may include at leastone extreme pressure additive. Nanoscale extreme pressure additives maybe added to lubricants disclosed herein in an amount greater than about0.1, 0.2, 0.3, and 0.5 weight percent in some embodiments, and less than10, 5, 2, and 1 weight percent in other embodiments.

In addition to those additives described above, additives that may alsofind use in improving the load carrying capacity of the lubricantsdisclosed herein include metals and borates, such as, for example,tungsten disulfide, boron nitride, monoaluminum phosphate, tantalumsulfide, iron telluride, zinconium sulfide, zinc sulfide, zinconiumnitride, zirconium chloride, bismuth sulfate, chromium boride, chromiumchloride, sodium tetraborate, tripotassium borate, zirconiumnaphthenate, zirconium 2-ethylhexanoate, zirconium 3,5-dimethylhexanoate, and zirconium neodecanoate. In one embodiment, the at leastone nanomaterial may comprise at least one of a metal, metal oxide,metal boride, and metal borate. Nanomaterial metals and/or borates maybe added to lubricants disclosed herein in an amount greater than about0.1, 0.2, 0.3, and 0.5 weight percent in some embodiments, and less than10, 5, 2, and 1 weight percent in other embodiments.

Additionally, for a review of common lubricant additives, see LubricantAdditives: Chemistry and Applications, edited by Leslie R. Rudnick(2003, ISBN 0824708571). Some of these additives include metaldeactivators, solubility aids, antioxidants, viscosifiers, etc. Metaldeactivators that may be incorporated in the lubricants disclosed hereinto act to protect against nonferrous corrosion may include, for example,benzotriazole, and its derivatives. Metal deactivators acting againstferrous corrosion may include, for example, alkylated organic acid andesters, organic acids, phenates, and sulfonates. Common solubility aids,which solubilize the additives into the oil or soap, may include, forexample esters, such as polyol esters, monoesters, diesters, andtrimellitate esters. Antioxidants used in grease formulations mayinclude, for example, substituted diphenylamines, amine phosphates,aromatic amines, butylated hydroxytoluene, phenolic compounds, zincdialkyl dithiophosphates, and phenothiazine. When a grease is utilizedto lubricate a rock bit, it is generally preferred not to employ a zincdialkyl dithiophosphate antioxidant if the rock bit comprises anincompatible metal, e.g., silver. In other lubricating applications,however, zinc dialkyl dithiophosphates may be employed as antioxidants.Additives that can be utilized in grease formulations for tackinessinclude polybutenes. In addition, viscosity index improvers, which helpto extend the operating range of the grease, may be used. Typicalviscosity index improvers include polybutene and polyisobutylenepolymers. Silicones or polymers can also be incorporated as antifoamagents and/or air entraimnent aids. A variety of dyes can also be usedto impart color to the grease. In addition, odor maskers such as pineoil can also be employed. Additionally, if the composition of thebasestock is predominantly synthetic oil, an ester-based swelling agentmay also be added to enhance the wetting and suspension of silica. Onesuitable swelling agent includes Esterex C4461, which is available fromExxonMobil Corporation (Fairfax, Va.).

Exemplary Formulations

In one embodiment of the present invention, the lubricant may include atleast one nanomaterial. Nanomaterial that may incorporated into thelubricants disclosed herein may include any solid additives among thosedescribed above. In a particular embodiment, nanomaterials that may beincorporated into the lubricants disclosed herein may include anyadditive that functions to improve the load carrying capacity of thelubricant. As used herein, the term nanomaterial refers to materialshaving a major dimension of less than 1000 nanometers. For sphericalparticles, the major dimension is the diameter of the sphere; fornon-spherical particles, the major dimension is the longest dimension.

In a particular embodiment, the nanomaterial may a scale ranging fromabout 0.1 to 100 nanometers. In another embodiment, the nanomaterial mayhave a scale ranging from 0.5 to 50 nanometers. In yet anotherembodiment, the nanomaterial may have a scale ranging from about 1.0 to10 nanometers. In another embodiment, the nanomaterial may have anaspect ratio ranging from 1.0 to 300. In yet another embodiment, thenanomaterial may have an aspect ratio ranging from 3.0 to 100.

In particular embodiments, the at least one nanomaterial may includemetal particles selected from at least one of lead, copper, silver, andaluminum. Metal particles may be added to lubricants disclosed herein inan amount greater than about 0.1, 0.2, 0.3, and 0.5 weight percent insome embodiments, and less than 10, 5, 2, and 1 weight percent in otherembodiments.

In other embodiment, the at least one nanomaterial may include metaloxide particles selected from at least one of lead oxide, zinc oxide,antimony trioxide, aluminum oxide, bismuth oxide, copper oxide. Metaloxide particles may be added to lubricants disclosed herein in an amountgreater than about 0.1, 0.2, 0.3, and 0.5 weight percent in someembodiments, and less than 10, 5, and 2 weight percent in otherembodiments.

In one embodiment, the at least one nanomaterial may include molybdenumdisulfide or other derivates thereof. Molybdenum sulfide particles maybe added to the lubricants disclosed herein in an amount greater thanabout 0.1, 0.2, 0.3, and 0.5 weight percent in some embodiments, andless than 10, 5, 2, and 1 weight percent in other embodiments.

In other embodiments, the at least one nanomaterial may include carbonnanostructures. Carbon nanostructures may include, for example, singlewall carbon nanotubes, multiwall carbon nanotubes, and vapor growncarbon fibers. Optionally, carbon nanotubes may be functionally treatedto alter the properties of the nanotube. In one embodiment, thelubricant may include a treated nanotube and at least one othernanomaterial. Carbon nanostructures may be added to lubricants disclosedherein in an amount greater than about 0.1, 0.2, 0.5 weight percent insome embodiments, and less than 10, 5, 2, and 1 weight percent in otherembodiments.

In a particular embodiment, the at least one nanomaterial may includepolarized graphite. Polarized graphite is described is U.S. PatentPublication No. 2005/0133265, which is incorporated by reference herein.Briefly, polarized graphite may be formed by treating graphite withalkali molybdates and/or tungstenates, alkali earth sulfates and/orphosphates and mixtures thereof to impart a polarized layer at thesurface of the graphite. Polarized graphite is available from DowCorning Corporation, Midland, Mich., under the tradename Lubolid®. Thelubricants disclosed herein may include polarized graphite in an amountgreater than about 0.1, 0.2, 0.3, and 0.5 weight percent in someembodiments, and less than 10, 5, 2, and 1 weight percent in otherembodiments.

In particular embodiments, the at least one nanomaterial may includediamond particles or diamond-like particles. One suitable method forgenerating nanodiamond may include, for example, a detonation process asdescribed in Diamond and Related Materials (1993, 160-2), which isincorporated by reference in its entirety, although nanodiamond producedby other methods may be used. Those having ordinary skill in the artwill appreciate how to form nanodiamond particles. Briefly, in order toproduce nanodiamond by detonation, detonation of mixed high explosivesin the presence of ultradispersed carbon condensate formsultradispersive diamond-graphite powder (diamond blend or DB), which isa black powder containing 40-60 weight percent of pure diamond. Chemicalpurification of DB generates pure nanodiamond (ultradispersivedetonational diamond or UDD), a grey powder containing up to 99.5 weightpercent of pure diamond. The ultrafine diamond particles generated bythe detonation process may comprise a nanodiamond core, a graphite innercoating around the core, and an amorphous carbon outer coating about thegraphite. Both the graphite coating and amorphous carbon coating may beoptionally removed by chemical etching. In some embodiments, thenanodiamond particles may be clustered in loose agglomerates ranging insize from nanoscale to larger than nanoscale. Diamond or diamond-likeparticles may be added to lubricants disclosed herein in an amountgreater than about 0.1, 0.2, 0.5 weight percent in some embodiments, andless than 10, 5, 2, and 1 weight percent in other embodiments.

In yet another embodiment, the at least one nanomaterial may include hBNparticles. HBN particles may be added to lubricants disclosed herein inan amount greater than about 0.1, 0.2, 0.5 weight percent in someembodiments, and less than 10, 5, 2, and 1 weight percent in otherembodiments.

In one embodiment, a lubricant may include from about 0.1 to about 10weight percent nanomaterial selected from at least one of lead, copper,silver, aluminum, lead oxide, zinc oxide, antimony trioxide, aluminumoxide, copper oxide, bismuth oxide, molybdenum disulfide, carbonnanostructures, polarized graphite, diamond, and hBN; about 1 to about10 weight percent of silica; about 5 to about 40 weight percent of athickening agent, preferably a metal-complex soap, and a balance of aheavy mineral basestock. In another embodiment, the lubricant mayfurther comprise at least one additional additive.

Application of the Lubricant in a Drill Bit:

Referring now FIGS. 1 and 2, a sealed bearing rotary cone rock bit,generally designated as 10, consists of bit body 12 forming an upper pinend 14 and a cutter end of roller cones 16 that are supported by legs 13extending from body 12. The threaded pin end 14 is adapted for assemblyonto a drill string (not shown) for drilling oil wells or the like. Eachof the legs 13 terminate in a shirttail portion 22. Each of the rollercones 16 typically have a plurality of cutting elements 17 pressedwithin holes formed in the surfaces of the cones for bearing on the rockformation to be drilled. Nozzles 20 in the bit body 12 introducedrilling mud into the space around the roller cones 16 for cooling andcarrying away formation chips drilled by the drill bit. While referenceis made to an insert-type bit, the scope of the present invention shouldnot be limited by any particular cutting structure. Embodiments of thepresent invention generally apply to any rock bit (whether roller cone,disc, etc.) that requires lubrication by grease.

Each roller cone 16 is in the form of a hollow, frustoconical steel bodyhaving cutting elements 17 pressed into holes on the external surface.For long life, the cutting elements may be tungsten carbide insertstipped with a polycrystalline diamond layer. Such tungsten carbideinserts provide the drilling action by engaging a subterranean rockformation as the rock bit is rotated. Some types of bits have hardfacedsteel teeth milled on the outside of the cone instead of carbideinserts.

Each leg 13 includes a journal 24 extending downwardly and radiallyinward on the rock bit body. The journal 24 includes a cylindricalbearing surface 25 which may have a flush hardmetal deposit 62 on alower potion of the journal 24.

The cavity in the cone 16 contains a cylindrical bearing surface 26. Afloating bearing 45 may be disposed between the cone and the journal.Alternatively, the cone may include a bearing deposit in a groove in thecone (not shown separately). The floating bearing 45 engages thehardmetal deposit 62 on the leg and provides the main bearing surfacefor the cone on the bit body. The end surface 33 of the journal 24carries the principal thrust loads of the cone 16 on the journal 24.Other types of bits, particularly for higher rotational speedapplications, may have roller bearings instead of the exemplary journalbearings illustrated herein.

A plurality of bearing balls 28 are fitted into complementary ball races29, 32 in the cone 16 and on the journal 24. These balls 28 are insertedthrough a ball passage 42, which extends through the journal 24 betweenthe bearing races and the exterior of the drill bit. A cone 16 is firstfitted on the journal 24, and then the bearing balls 28 are insertedthrough the ball passage 42. The balls 28 carry any thrust loads tendingto remove the cone 16 from the journal 24 and thereby retain the cone 16on the journal 24. The balls 28 are retained in the races by a ballretainer 64 inserted through the ball passage 42 after the balls are inplace. A plug 44 is then welded into the end of the ball passage 42 tokeep the ball retainer 64 in place.

Contained within bit body 12 is a grease reservoir system generallydesignated as 18. Lubricant passages 21 and 42 are provided from thereservoir to bearing surfaces 25, 26 formed between a journal bearing 24and each of the cones 16. Drilling fluid is directed within the hollowpin end 14 of the bit 10 to an interior plenum chamber 11 formed by thebit body 12. The fluid is then directed out of the bit through the oneor more nozzles 20.

The bearing surfaces between the journal 24 and cone 16 are lubricatedby a lubricant or grease composition. Preferably, the interior of thedrill bit is evacuated, and lubricant or grease is introduced through afill passage 46. The lubricant or grease thus fills the regions adjacentthe bearing surfaces plus various passages and a grease reservoir. Thegrease reservoir comprises a chamber 19 in the bit body 10, which isconnected to the ball passage 42 by a lubricant passage 21. Lubricant orgrease also fills the portion of the ball passage 42 adjacent the ballretainer. Lubricant or grease is retained in the bearing structure by aresilient seal 50 between the cone 16 and journal 24.

Lubricant contained within chamber 19 of the reservoir is directedthrough lube passage 21 formed within leg 13. A smaller concentricspindle or pilot bearing 31 extends from end 33 of the journal bearing24 and is retained within a complimentary bearing formed within thecone. A seal generally designated as 50 is positioned within a sealgland formed between the journal 24 and the cone 16.

In one embodiment, the lubricant or grease in the grease reservoir mayinclude from about 0.1 to about 10 weight percent of a nanomaterialselected from at least one of lead, copper, silver, aluminum, leadoxide, zinc oxide, antimony trioxide, aluminum oxide, copper oxide,bismuth oxide, molybdenum disulfide, carbon nanostructures, polarizedgraphite, diamond, and hBN; about 1 to about 10 weight percent ofsilica; about 5 to about 40 weight percent of a thickening agent,preferably a metal-complex soap, and a balance of a basestock. Inanother embodiment, the lubricant may further comprise at least oneadditional additive. In yet another embodiment, the basestock may be ablend of 0 to 100% mineral oil and 100 to 0% synthetic oil with anypercentage therebetween, preferably about 50% of each.

Use of the Lubricant in a Method of Drilling:

According to one aspect of the present invention, a method for drillingis provided. In one embodiment, the method for drilling includes thesteps of providing a roller cone drill bit having a bit body and aplurality of roller cones mount on the bit body with rotatable journalbearings, introducing a lubricating composition to the journal bearings,where the lubricating composition includes a basestock, a thickener, andat least one nanomaterial. In one embodiment, the lubricant in thegrease reservoir may include from about 0.1 to about 10 weight percentof a nanomaterial selected at least one of lead, copper, silver,aluminum, lead oxide, zinc oxide, antimony trioxide, aluminum oxide,copper oxide, bismuth oxide, molybdenum disulfide, carbonnanostructures, polarized graphite, diamond, and hBN; about 1 to about10 weight percent of silica; about 5 to about 40 weight percent of athickening agent, preferably a metal-complex soap, and a balance of abasestock. In another embodiment, the lubricant may further comprise atleast one additional additive. In yet another embodiment, the basestockmay be a blend of 0 to 100% mineral oil and 100 to 0% synthetic oil withany percentage therebetween, preferably about 50% of each.

A vast number and variety of rock bits can be satisfactorily lubricatedwith grease compositions of preferred embodiments. The greases ofpreferred embodiments may also comprise a variety of additives notspecifically mentioned above. For example, the grease can contain typesof extreme pressure agents, corrosion inhibitors, oxidation inhibitors,anti-wear additives, pour point depressants, and thickening agents notenumerated above. In addition, the grease composition can compriseadditives not specifically mentioned such as water repellants, anti-foamagents, color stabilizers, and the like. Also, while the greases ofpreferred embodiments can be particularly well suited for rock bitlubrication, they can also be suitable for use in other applications,such as bearing lubrication, for example, automotive bearing lubrication(e.g., lubrication of belt tensioner bearings, bearings for fan belts,water pumps, and other under-the-hood engine components), other hightemperature and/or high speed bearing lubrication applications, and thelike. The greases of preferred embodiments are suitable for use asmultipurpose greases in many high temperature applications.

Advantageously, embodiments of the present invention may include one ormore of the following. The incorporation of nanomaterials may improvethermal performance including thermal breakdown and conductivity.Increases in the load bearing capacity may also be achieved which mayalso lead to increases in rate of penetration and the life of thebearing. Various additives may also add corrosion resistance to a metalsurface to which the lubricant may be applied. The lubricants may alsoaid in reducing the hub wear and improve seal appearance with lowleakage rates. The range of applicability for the nanomaterialsdisclosed herein may also allow them to be used with a variety ofexisting grease compositions to improve lubricantion properties andbroaden the applicable uses of the greases to otherwise non-applicableuses, such as drilling.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A lubricant for a drill bit, comprising: from about 0.1 to about 10weight percent of at least one nanomaterial; from about 5 to 40 weightpercent of a thickener; and a basestock.
 2. The lubricant of claim 1,further comprising: at least one additive selected from corrosioninhibitors, antioxidants, antiwear additives, extreme pressure agents,and lubricity additives.
 3. The lubricant of claim 1, wherein thebasestock comprises from 0 to 100 percent mineral oil and 100 to 0percent synthetic oil, or any percentage therebetween.
 4. The lubricantof claim 1, wherein the at least one nanomaterial comprises diamondparticles.
 5. The lubricant of claim 4, wherein the diamond particlescomprise: a diamond core; and a non-diamond carbon-based coating on thediamond core.
 6. The lubricant of claim 5, wherein the carbon-basedcoating comprises an inner coating of graphite and an outer coating ofamorphous carbon.
 7. The lubricant of claim 1, wherein the at least onenanomaterial comprises carbon nanotubes.
 8. The lubricant of claim 7,wherein the at least one nanomaterial comprises treated carbonnanotubes.
 9. The lubricant of claim 1, wherein the at least onenanomaterial comprises at least one selected from copper particles,polarized graphite, molybdenum disulfide, antimony oxide, bismuth oxide.10. A roller cone drill bit, comprising: a bit body; at least one legextending downward from the bit body, wherein each leg has a journal andeach journal has a bearing surface; a roller cone mounted on eachjournal, wherein each roller cone has a bearing surface; a greasereservoir in communication with the bearing surfaces; and a lubricatingcomposition in the grease reservoir and adjacent the bearing surfaces,the lubricating composition comprising: from about 0.1 to about 10weight percent of at least one nanomaterial; from about 5 to 40 weightpercent of a thickener; and a basestock.
 11. The drill bit of claim 9,wherein the basestock comprises from 0 to 100 percent mineral oil and100 to 0 percent synthetic oil, or any percentage therebetween.
 12. Thedrill bit of claim 9, wherein the at least one nanomaterial comprisesdiamond particles.
 13. The drill bit of claim 11, wherein the diamondparticles comprise: a diamond core; and a non-diamond carbon-basedcoating on the diamond core.
 14. The drill bit of claim 12, wherein thecarbon-based coating comprises an inner coating of graphite and an outercoating of amorphous carbon.
 15. The drill bit of claim 9, wherein theat least one nanomaterial comprises carbon nanotubes.
 16. The drill bitof claim 9, wherein the at least one nanomaterial comprises at least oneselected from copper particles, polarized graphite, molybdenumdisulfide, antimony oxide, bismuth oxide.
 17. A method for lubricating aroller cone drill bit, comprising: providing a roller cone drill bithaving a bit body, a grease reservoir, and at least one roller conemounted on the bit body with at least one rotatable journal bearing; andfilling the grease reservoir with a lubricant, the lubricant comprising:from about 0.1 to about 10 weight percent of at least one nanomaterial;from about 5 to 40 weight percent of a thickener; and a basestock. 18.The method of claim 16, wherein the basestock comprises from 0 to 100percent mineral oil and 100 to 0 percent synthetic oil, or anypercentage therebetween.
 19. The method of claim 16, wherein the atleast one nanomaterial comprises diamond particles.
 20. The method ofclaim 18, wherein the diamond particles comprise: a diamond core; and anon-diamond carbon-based coating on the diamond core.
 21. The method ofclaim 19, wherein the carbon-based coating comprises an inner coating ofgraphite and an outer coating of amorphous carbon.
 22. The method ofclaim 16, wherein the at least one nanomaterial comprises carbonnanotubes.
 23. The method of claim 16, wherein the at least onenanomaterial comprises at least one selected from copper particles,polarized graphite, molybdenum disulfide, antimony oxide, bismuth oxide.